1. Field of the Invention
The present invention relates to an ultrasonic transducer, and more particularly, it relates to an improvement in the structure of an ultrasonic transducer employing a piezoelectric element, such that the transducer can be reduced in thickness.
2. Description of the Prior Art
A drop-proof ultrasonic transducer may be employed in a sensor in an automobile for detecting an obstruction and informing the driver of the same, in case of backing the automobile, for example. Such a transducer performs the functions of transmitting and receiving ultrasonic waves such that, when some obstruction is present in a direction to which the ultrasonic wave is transmitted, the ultrasonic wave transmitted from the transducer is reflected by the obstruction and is received by the same transducer, which thereby detects the presence of the obstruction. Further, the distance between the obstruction and the transducer can be determined by measuring the time from transmission of the ultrasonic wave to receiving of the same by way of the reflection.
A piezoelectric ultrasonic transducer of background interest to the present invention is disclosed in U.S. Pat. No. 4,556,814 issued on Dec. 3, 1985 and granted to Ito et al. In said U.S. Patent, a piezoelectric element is bonded to the inner surface of a top wall of a housing member which has an inverted U-shaped cross-section, while the bottom surface of the housing member is closed by a cover plate. Lead wires are respectively connected to two electrodes of the piezoelectric element for inputting and outputting signals, which lead wires are respectively connected to a pair of terminal pins passing through the cover plate.
The aforementioned transducer operates through bending vibration of the top wall of the housing member. Therefore, the vertical size of the side wall of the housing member must be as large as possible in order to reduce leakage of the bending vibration to the minimum. This prior art patent also discloses an embodiment in which a tubular member having relatively high acoustic impedance is connected to the side wall in order to reduce the decay time caused by transmission of vibration generated in the top wall to the side wall and the cover plate mechanically fixed to the same, thereby to improve a vibration damping effect in the side wall of the housing member.
In the prior art as disclosed in the aforementioned U.S. Patent, the size of transducer is increased since the side wall of the housing member has a large height. Further, assembly of the transducer is complicated in the structure provided with the tubular member.